The goal of this study is to investigate the possibility of using marker-assisted selection of superior embryos to increase pregnancy rates following transfer of in vitro-derived blastocysts. Such a strategy could have a significant impact on the treatment of fertility problems in humans, where pregnancy rates after in vitro fertilization and transfer of early stage embryos have remained well below 25%. An investigation of the feasibility of marker-assisted embryo selection requires a large number of embryos and recipients under controlled conditions, criteria that are unlikely to be met for human embryos. It is, therefore, proposed to use the secretion of interferon-tau (IFN-t) by bovine blastocysts as a model system to examine the hypothesis that the level of a protein produced by an individual embryo can be a useful predictor of its developmental competence. The IFN-t are Type 1 interferons that are expressed and secreted by the embryos of cattle and sheep during early pregnancy and while their precise physiological role remains unclear, there is mounting evidence implicating these interferons in the mechanism of pregnancy recognition. IFN-t can be easily detected in the culture medium of in vitro-derived bovine blastocyst, but there exists virtually no information on the significance of the observation that individual blastocysts can produce vastly different amounts of IFN-t. The aims of this proposal, therefore, are to gain further understanding of IFN-t production in embryos as well as its significance for subsequent development. Specific questions to be addressed are: 1) can culture conditions affect IFN-t production; 2) are there genotypic effects on its production; 3) does the amount of IFN-t produced by in vitro-derived blastocysts differ from that of blastocysts generated in vivo, and what is the nature of the increase in interferon-t that is found in blastocysts that are older at blastulation; 4) is IFN-t imprinted or does the amount of IFN-t that is produced by parthenogenetic and androgenetic blastocysts differ from that of control embryos, and lastly, 5) can the amount of IFN-t that is secreted in culture be a useful aid to predict the likelihood of pregnancy following transfer into recipients.